This invention relates to an interface unit for vacuum sewage systems.
Vacuum sewage systems are used to replace conventional gravity sewers in areas having such problems as hilly or rocky terrain, low population density, adverse grade conditions, high water table or flat land. Where such problems exist, vacuum sewage systems are often a very attractive, economical alternative to conventional systems.
Conventional plumbing fixtures can be used within the dwelling, or other source of sewage, and a conventional gravity line leads therefrom. At each source of sewage, an interface unit is used to connect the conven-tional plumbing to the vacuum sewage system. From this point, the sewage is propelled through the vacuum main to a central collecting station, located, typically, up to a mile away from the interface unit. From the collecting station, the sewage is discharged, for example, to a gravity sewer, force main, treatment plant or lagoon.
At the end of the gravity pipe leading from each building or group of buildings, an accumulation enclosure is used to batch a volume of liquid for admission into the vacuum system. The accumulation enclosure may simply be a horizontal extension of the gravity fed pipe at a slightly lower elevation. Alternatively, a tank or other container may be used for the accumulation enclosure. The vacuum sewage conduit is usually smaller in diameter than the gravity feed pipe and is located closer to ground level.
Conventionally, the interface unit includes a cylindrical chamber which extends downwardly from ground level to the accumulation enclosure. Within the enclosure, a suction tube or vacuum conduit extension extends downwardly from the vacuum conduit to the accumulation enclosure. Where the accumulation enclosure is a pipe having the same diameter as the gravity feed conduit, a reducer coupling connects the accumulation enclosure to the vacuum conduit extension. There is a vacuum-activated valve on the vacuum conduit. The valve is normally closed, but is opened when a sensor unit, connected to the accumulation enclosure, senses a predetermined hydrostatic pressure. Consequently, when a batch of sewage has accumulated in the accumulation enclosure, the sensor unit causes the valve to open and allows the batch of sewage to flow upwardly through the vacuum conduit extension to the vacuum conduit and the vacuum sewage system. The valve is closed at the end of a timed cycle or upon a drop of hydrostatic pressure within the accumulation enclosure to a specified level.
In the conventional interface unit described above, blockage is most likely to occur at the reducer coupling between the accumulation enclosure and the bottom of the vacuum conduit extension. A cleanout plug is normally provided adjacent the reducer in case a blockage should occur. To give access to this cleanout plug, the chamber enclosing the interface unit is desirably extended downwardly to the level of the accumulation enclosure and the cleanout plug.
To reduce the cost of the interface units, one approach has been to shorten the chamber so that it encloses only the end of the vacuum conduit, the valve and the sensor. However, this means that, should a blockage occur at the reducer coupling, the soil above the reducer must be excavated at a considerable cost and inconvenience. Additionally, with this arrangement, there must be a separate conduit from the sensor unit to the accumulator enclosure.
The depth of the interface chamber, and, consequently, the cost of the interface unit, could both be reduced if the reducer coupling could be raised to the level of the end of the vacuum conduit by increasing the size of the vacuum conduit extension to that of the gravity feed conduit and the accumulation enclosure. However, where this has been attempted, the surge of sewage through this relatively large diameter section of pipe to the valve causes unacceptable hammering against the valve or the restriction in the pipe.
For the reasons given above, it would be desirable to have an interface unit which would require only a relatively short chamber at ground level to enclose the valve and sensor unit, but would give access to the point of restriction between the accumulation enclosure and the smaller diameter vacuum conduit extension. At the same time, it would be desirable to eliminate the need for a separate downwardly extending conduit from the sensor to the accumulation enclosure.